1. Field of the invention
This invention relates to a thermal recording apparatus for recording image information on a thermo-sensitive recording medium with a laser beam irradiated thereto, and more specifically to a thermal recording apparatus provided with means for avoiding in advance inconveniences developed in a thermo-sensitive recording medium or the apparatus owing to an abnormality in the operation of the apparatus.
2. Description of the Related Art
A thermal recording apparatus for recording image information on a thermo-sensitive recording medium by applying heat energy thereto has been widespread. In particular, an apparatus of this type, provided with a laser beam as the heat source and capable of recording an image at a high speed, has been proposed (see Japanese Laid-Open Patent Publication Nos. 50-23617, 58-94494, 62-77983 and 62-78964, for example).
The present applicant has developed and applied for a patent a thermo-sensitive recording medium applicable to such a thermal recording apparatus and capable of recording high quality images thereon, which comprises leuco dyes, a developer and light-absorbing dyes, all provided on a support member, and develops color at a density responsive to the heat energy applied thereto (see Japanese Patent Application No. 3-62684 and Japanese Laid-Open Patent Publication No. 5-24219).
The thermo-sensitive recording medium comprises a thermo-sensitive layer formed on a support member by applying thereto a coating liquid containing a developer and light-absorbing dyes, together with microcapsules containing at least leuco dye, dissolved in an organic solvent insoluble or hardly soluble in water, and thereafter dispersed and emulsified in an aqueous medium.
The leuco dyes have the property of donating electrons, or accepting protons from acid, in developing color. The leuco dyes are normally substantially colorless and have partial skeletons such as lactone, lactam, sultone, spiropyran, ester, amide, etc. which allow to open rings or produce cleavages when held in contact with the developer. Specific examples of the leuco dyes may include crystal violet lactone, benzoyl leucomethylene blue, malachite green lactone, rhodamine B lactam, 1,3,3-trimethyl-6'-ethyl-8'-butoxyindolinobenzo spiropyran, etc.
Acidic substances such as phenolic compounds, organic acids or metallic salt containing the same, oxybenzoate ester, etc. are used as developers corresponding to these leuco dyes. The developers may preferably have a melting point ranging from 50.degree. C. to 250.degree. C. Particularly preferred is phenol or an organic acid insoluble in water, having a melting point ranging from 60.degree. C. to 200.degree. C. Specific examples of the developers have been described in Japanese Laid-Open Patent Publication No. 61-291183, for example.
Preferred as the light-absorbing dyes are those which absorb less light in the visible-light wavelength region and exhibit particularly a high absorption rate for radiation in the infrared wavelength region. Examples of the light-absorbing dyes may include cyanine dyes, phthalocyanine dyes, pyrylium and thiopyrylium dyes, azulenium dyes, squarylium dyes, metal complex dyes containing Ni, Cr, etc., naphthoquinone and anthraquinone dyes, indophenol dyes, indoaniline dyes, triphenyl- methane dyes, triallylmethane dyes, ammonium and diammonium dyes, nitroso compounds, etc. Of these, it is preferable to use those having a high absorption rate for light of a wavelength ranging from 700 nm to 900 nm in the near infrared region, on account of that a semiconductor laser for near infrared light has been put to practical use.